Abrasion resistant coatings on a substrate are known in the art. These coatings are typically scratch resistant and resistant to attack by chemical and organic solvents. Typically, the coatings are curable either thermally or by radiation.
Thermal curing systems require removal of solvents and require provision of heat to process the coating. These requirements increase cost for energy consumption and protection of the environment. Of course, use of thermal curing systems on heat sensitive materials is precluded by the very nature of the process. Continuous processing using thermal curing systems is difficult because such systems are not readily adaptable to rapid continuous processing. Simply, thermally curing systems require heat and residence time in curing ovens to effect polymerization of an abrasion resistant coating.
It has been discovered that radiation curing systems overcome the disadvantages of thermal curing systems. Radiation curing systems have the advantage of reducing energy costs and environmental problems, reducing processing temperatures and processing times compared with thermal curing systems.
Thick coatings that are radiation curable are known in the art. It is known that a first monomer selected from the group consisting of triacrylates and tetraacrylates has been mixed with a second monomer having a N-vinyl imido group and then subjected to radiation curing. These coatings have been applied to various substrates. Typical coating thicknesses have been 1 to 25 microns. Thicker coatings have been necessary to obtain maximum abrasion resistance. These generally thick coatings have precluded certain uses for the coating.
U.S. Pat. No. 4,308,119 also relates to a radiation curable coating composition applicable to a variety of substrates. The coating composition comprises a pentaerythritol polyacrylate or polymethacrylate, such as pentaerythritol tetraacrylate, cellulose ester and a photoinitiator. Thick coatings are obtained by using the teachings of this patent even with spraying a coating thickness on the order of 0.1 to 1.5 mils.
An historic technique utilizes a composite energy control sheet. The sheet includes a semi-transparent reflective metal layer which is coated on a self-supporting polymeric foil and protectively covered with a transparent polymeric layer. Suitable polymers for the polymeric layer are polyethylene, polypropylene and polyacrylonitrile. However, polymers having low infrared radiation transmission properties and high infrared radiation absorption properties are disadvantageous. The thickness of the layer is preferably about 10 microns for adequate abrasion resistance. When the protective layer is applied by coating from a solvent, 5 to 15 microns is a fairly typical thickness, but thicknesses as great as 25 to 50 microns can be employed. Thicknesses less than 10 microns result in substantially reduced abrasion resistance.
The present invention discloses a superior coating formulation, method of application and product thereof which overcomes the disadvantages of the prior art and which has optimum abrasion resistance and minimal infrared absorption thereby achieving a superior insulating film or structure for use, for example, in windows.